There is a large interest in recycling waste materials, rather than storing them in landfills. This is particularly true with respect to used tires, a post-consumer waste product, and waste materials resulting from tire manufacture, a post-industrial waste product. Combustion of these materials can produce harmful gases, as they include sulfur crosslinks (a process known as vulcanization), which form hydrogen sulfide on combustion.
There are a variety of processes for depolymerizing the rubber in used tires, including those disclosed in EP 0694600 and U.S. Pat. No. 7,628,892. EP 0694600 discloses a process and a plant where used tires are depolymerized at relatively low pressure, and at a temperature between 100 and 135° C., to form gas and liquid products, which are subsequently combusted. The temperature is maintained by introducing water and air in the device.
U.S. Pat. No. 7,628,892 discloses a plant which includes a depolymerizing device, with a substantially cylindrical body, with an upper base, and a lower base. Thermal depolymerization of tires occurs inside the device, and a product mixture exits the device and then enters a phase separator, to separate out liquid products from gaseous products. The phase separator is connected to an aspiration unit, which enables the depolymerizing device to operate at pressures up to 10 mBar lower than atmospheric pressure. The process purportedly produces a carbonaceous fuel product, and a gaseous product which is burned.
The '892 patent also discloses adding calcium oxide to tires, such that, as the rubber in the tires is depolymerized in the presence of steam, the calcium oxide is converted to calcium hydroxide, which then reacts with sulfur, and forms a salt that then mixes with the steel and carbon recovered from the depolymerization process.
It would be advantageous to provide improved devices and processes for thermally de-manufacturing tires and other waste streams, which in some embodiments do not require added calcium salts to react with sulfur used in rubber vulcanization processes, and which allow for desulfurization to occur, if such is desired, outside of the retort chamber.